1. Field of the Invention
The present invention relates to a method for joining an immersion nozzle used when molten metal is made to flow out from a molten metal vessel, and more specifically, to a method for joining the upper surface of an immersion nozzle to a lower plate brick or to a lower nozzle.
2. Description of the Related Art
Since the lower portion of an immersion nozzle used in a continuous casting apparatus is continuously immersed in and eroded by molten metal, when it becomes necessary, it must be replaced with a new immersion nozzle. Therefore, the immersion nozzle is joined to either the lower plate brick of a sliding nozzle or a lower nozzle which is located above the immersion nozzle, by method that makes replacement possible.
For example, when the upper surface of an immersion nozzle is joined to the lower plate brick of a sliding nozzle or to a lower nozzle, a method of inserting packing between the joining surfaces has conventionally been employed. According to this method, packing is set on the preheated immersion nozzle and the immersion nozzle is joined with the lower plate brick or the lower nozzle. The packing is composed of a packing material or a filler which is disclosed in, for example, Japanese Patent Publication No. 61-14111, Japanese Patent Laid-Open No. 4-154676, Japanese Patent Laid-No. 5-163073 and Japanese Patent Laid-Open No. 5-163074.
This method, however, has problems in that the work environment is deteriorated, the joining operation cannot be confirmed visually, etc., because, after the packing is set to the preheated immersion nozzle, smoke and bad smells are generated from the binder when the immersion nozzle is joined with the lower plate brick or the lower nozzle. Also, between the time that packing is set to the preheated nozzle and the nozzle is joined with the lower plate brick or the lower nozzle the packing is heat cured, and problems such as the sealing property becoming poor, air suction, molten steel leakage, and abnormally melting of nozzle bricks occur.
Although a method of pre-bonding or mounting a packing to the lower plate brick or the lower nozzle and joining it with the preheated immersion nozzle is also used, this method has problems in that the joining operation cannot be visually confirmed and the parts cannot be automatically joined using a sensor because the heat of the immersion nozzle causes the packing to generate smoke.
To solve the aforesaid problems when packing is used, a method of providing a plate-shaped sliding portion on the upper portion of the immersion nozzle and pressing it against a sliding plane surface portion formed on the lower portion of the lower plate brick or the lower nozzle is used. This method is advantageous in that since no packing is necessary in the portion where the immersion nozzle and lower plate brick or the lower nozzle are joined, the immersion nozzle can be replaced in a short time. Thus, this method is employed in the immersion nozzle replacing apparatus disclosed in, for example, U.S. Pat. No. 4,669,528.
However, since the portion where the immersion nozzle and the lower plate brick or the lower nozzle are joined is required to have sealing properties to prevent oxidation of molten steel due to gas being sucked into the immersion nozzle and the like, the plate-shaped sliding portion formed on the upper portion of the immersion nozzle and the sliding plane surface portion formed on the lower portion of the lower plate brick or the lower nozzle must be smoothly finished. This is to prevent the suction of the gas when the immersion nozzle is pressed against the lower plate brick or the lower nozzle. The cost is thus increased by this smooth finish machining. In addition, the immersion nozzle and the lower plate brick or the lower nozzle which have been smoothly finished must be carefully handled so that the sliding portions are not damaged.
Further, there is a fear that the sealing properties of the immersion nozzle replacing apparatus disclosed in, for example, U.S. Pat. No. 4,669,528 can be lowered. This is caused when the immersion nozzle is replaced. Since the plate-shaped sliding portion formed on the upper portion of the immersion nozzle and the sliding plane surface portion formed on the lower portion of the lower plate brick or the lower nozzle move in a state of contact with each other, there is the danger that the sliding portions of both parts may be damaged during replacement and their smooth finish become scratched, resulting in that when both parts are pressed against each other, gaps will be formed by the scratches.